Biotic resistance, the process by which new colonists are excluded from a community by predation from and/or competition with resident species, can prevent or limit species invasions. We examined whether biotic resistance by native predators on Caribbean coral reefs has influenced the invasion success of red lionfishes (Pterois volitans and Pterois miles), piscivores from the Indo-Pacific. Specifically, we surveyed the abundance (density and biomass) of lionfish and native predatory fishes that could interact with lionfish (either through predation or competition) on 71 reefs in three biogeographic regions of the Caribbean. We recorded protection status of the reefs, and abiotic variables including depth, habitat type, and wind/wave exposure at each site. We found no relationship between the density or biomass of lionfish and that of native predators. However, lionfish densities were significantly lower on windward sites, potentially because of habitat preferences, and in marine protected areas, most likely because of ongoing removal efforts by reserve managers. Our results suggest that interactions with native predators do not influence the colonization or post-establishment population density of invasive lionfish on Caribbean reefs.

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Indo-Pacific lionfish have invaded large parts of the western Atlantic, Caribbean and Gulf of Mexico, and have already caused measurable declines in native Atlantic reef fauna. Culling efforts are occurring across the region, particularly on coral reefs, to reduce local lionfish abundances. Frequent culling has recently been shown to cause a shift towards more wary and reclusive behaviour by lionfish, which has prompted calls for halting culls. However, the effectiveness of culling per se is not in question. Culling successfully lowers lionfish numbers and has been shown to stabilise or even reverse declines in native prey fish. In fact, partial culling is often as effective as complete local eradication, yet requires significantly less time and effort. Abandoning culling altogether would therefore be seriously misguided and a hindrance to conservation. We offer suggestions for how to design removal programs that minimize behavioural changes and maximize culling success.

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